Optoelectronic shutters are well known in the art. Such shutters open and shut in response to an electrical waveform or pulse applied thereto, generally without moving mechanical parts. They are used, inter alia, in high-speed image capture applications, for which mechanical shutters are typically too slow. Optoelectronic shutters known in the art include liquid crystal shutters, electrooptical crystal shutters and gated image intensifiers.
Liquid crystal shutters are simple and inexpensive to manufacture. Their speed, however, is inherently limited to about 20 microsecond switching time. Moreover, in their open state, liquid crystal shutters typically transmit only about 40% of the light incident thereon, whereas in their closed state, they still transmit at least 0.1% of the incident light.
Electrooptical crystal shutters can be switched quickly, on the order of 0.1 nanosecond. They require a collimated light input, however, and have only a narrow acceptance angle within which they can shutter incident light efficiently. The crystals themselves are expensive, and costly, high-speed, high-voltage electronics are also needed to switch the shutters on and off at the rated speed. However, shutters using microchannel plates are generally non-linear at high frequencies.
Image intensifiers generally comprise an electron tube and microchannel plate, with a photoelectric photocathode input and a light-emitting phosphor-coated anode at the output. Gated intensifiers further include high-speed switching circuitry, which enables them to be gated on and off quickly, with typical switching times as fast as 1 nanosecond. For light to be effectively shuttered or amplified by the intensifier, it must be focused on the photocathode. Although intensifiers are manufactured in large quantities, the manufacturing process involves attachment of high-voltage feed-through electrode and metal-to-glass sealing, which is complex, labor intensive and therefore costly. Partly as a result of this complexity, gated intensifiers tend to be large and are available in a very limited range of shapes and sizes.
GB 2 082 830 describes an electron beam shutter device that forms an image of a luminous event changing at high speed. FIGS. 1 and 2 of the reference show devices with electrostatic focusing. FIG. 3 shows a device in which the image resolution is low (i.e., the image is defocused and FIGS. 4-8 show a device utilizing a micro-channel plate. With respect to FIG. 3, it is believed that the defocusing is caused by the distance required between the cathode and anode due to the construction of the device.
U.S. Pat. No. 4,220,975 shows a shutter device in which a microchannel plate is used.